The Nightmaretaker Guide

The Dark Stalker passive (Vampire) or Fleet Phantom (Champion Points) helps you move faster while sneaking.

That is when you know you are approaching the core. the nightmaretaker guide

The Nightmaretaker doesn't deal direct damage initially. Instead, they apply "Phobia Stacks." As these stacks build, the screen may flicker, controls may become sluggish, or illusory enemies may appear. At maximum stacks, the victim enters a "Terror State," taking massive periodic damage. B. Shadow Stepping The Dark Stalker passive (Vampire) or Fleet Phantom